Image pickup device, microscope image pickup system, and endoscope image pickup system

ABSTRACT

Provided is a medical imaging device comprising: a color separation prism that has a dichroic film configured to split light into first light belonging to a visible light wavelength band and second light belonging to a fluorescence wavelength band; a fluorescence image sensor that is provided at an output side of the color separation prism and that is configured to image at least part of the second light belonging to the fluorescence wavelength band separated by the dichroic film; a visible light image sensor that is provided at the output side of the color separation prism and that is configured to image at least part of the first light belonging to the visible light wavelength band separated by the dichroic film; and a bandpass filter that is disposed between the color separation prism and the fluorescence image sensor, wherein the fluorescence image sensor and the visible light image sensor are arranged such that an optical path difference between an optical path length of a fluorescence optical path for the second light imaged on the fluorescence image sensor via the color separation prism and an optical path length of a visible light optical path for the first light imaged on the visible light image sensor via the color separation prism corresponds to an amount of a shift between a fluorescence imaging position and a visible light imaging position, the shift being generated by an imaging lens positioned at an input side of the color separation prism, and wherein the fluorescence imaging position is an imaging position of filtered second light, which results from passing the second light through the bandpass tiller, such that tlic amoiuu of shifl is based on the filtered second light.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Japanese Priority PatentApplication JP 2015-175569 filed Sep. 7, 2015, the entire contents ofwhich are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to an image pickup device, a microscopeimage pickup system, and an endoscope image pickup system.

BACKGROUND ART

There is known a technology (photodynamic diagnosis/treatmenttechnology) for ad-ministering any of various fluorescent probes to apatient, emitting excitation light for exciting the fluorescent probewhen the fluorescent probe is accumulated on a cancer tissue or thelike, observing near-infrared fluorescence having a predeterminedwavelength emitted from the fluorescent probe to specify a position ofan affected part (that is, the cancer tissue) to thereby performdiagnosis and treatment. A wavelength of the excitation light forexciting the fluorescent probe and a wavelength of the near-infraredfluorescence emitted from the fluorescent probe are inherent to afluorescent probe to be used, and, in the case where, for example,indocyanine green is used as a fluorescent probe, light having awavelength of about 769 nm is used as excitation light, and fluorescencehaving a wavelength of about 832 nm is emitted from indocyanine green.

In the above photodynamic diagnosis/treatment technology, fluorescenceis observed in a dark state in which indoor lighting is off becauseobtainable fluorescence intensity is weak. Thus, a doctor recognizes animage in which a fluorescence part is luminous in a dark field ofvision, and therefore it is difficult to specify a position of thefluorescence part in the whole affected part. As a result, the doctorrecognizes the affected part while switching observation with visiblelight and observation with fluorescence and then implements diagnosis ortreatment. Thus, processing is complicated. In order to solve such acircumstance, various matters of an image pickup system for performingsuperimposed display of a fluorescence image and a visible light imagein real time have been studied.

For example, PTL 1 cited below discloses a microscope system including:branch optical mechanism for dividing, into two parts, an observedluminous flux extracted to the outside from an affected part to which afluorescent probe has been administered; fluorescence image pickupmechanism connected to one end of the branch optical mechanism; andvisible light image pickup mechanism connected to the other end of thebranch optical mechanism; and display mechanism for displaying afluorescence image captured by the fluorescence image pickup mechanismand a visible light image captured by the visible light image pickupmechanism so that the fluorescence image and the visible light image aresuperimposed, in which the branch optical mechanism is an optical blockhaving an interface for coaxially separating only fluorescence having apredetermined wavelength from visible light in the observed luminousflux.

PTL 2 described below discloses a near-infrared fluorescence detectiondevice for detecting near-infrared fluorescence from a fluorescentmaterial accumulated on a sentinel lymph node inside a body. Morespecifically, the near-infrared fluorescence detection device splitsreflected light and near-infrared fluorescence from an observationtarget into visible-light reflected light and near-infrared fluorescenceby using a beam splitter such as a dichroic prism, then detects thevisible reflection light and the near-infrared fluorescence to therebyform a visible reflection light image signal and a near-infraredfluorescence signal, and outputs a composite image obtained by combiningthe visible-light video signal and the near-infrared fluorescencesignal. Herein, PTL 2 cited below discloses that visible reflectionlight is detected by a color image sensor, whereas near-infraredfluorescence is detected by a monochrome image sensor, and themonochrome image sensor is disposed to be isolated from the beamsplitter at a predetermined distance (A), as compared with the colorimage sensor, in order to correct axial chromatic aberration.

CITATION LIST Patent Literature

PTL 1: JP 2013-3495A

PTL 2: JP 2015-16332A

SUMMARY Technical Problem

However, in PTL 1 cited above, because only a fluorescence component isattempted to be extracted from an incident observed luminous flux byusing only an optical multilayer film having a characteristic that “thebranch optical mechanism is an optical block having an interface forcoaxially separating only fluorescence having a predetermined wavelengthfrom visible light in the observed luminous flux”, costs formanufacturing the optical multilayer film are increased and a desiredspectral characteristic is not achieved.

PTL 2 cited above neither discloses a condition that is necessary for aspectral characteristic of the beam splitter for splitting near-infraredfluorescence nor a method of achieving an isolation distance Δ.Therefore, depending on a spectral characteristic of fluorescence fromthe observation target, axial chromatic aberration is not completelycorrected and a favorable superimposed image is not obtained.

As described above, in the technologies disclosed in PTL 1 and PTL 2cited above, light from an observation target is not split into avisible light component and a fluorescence component with high accuracy,and a favorable superimposed image obtained by superimposing a visiblelight image and a fluorescence image is not obtained.

In view of the above circumstances, embodiments of the presentdisclosure propose an image pickup device, a microscope image pickupsystem, and an endoscope image pickup system, each of which is capableof splitting light from an observation target into a visible lightcomponent and a fluorescence component with high accuracy and is capableof obtaining a favorable superimposed image by superimposing a visiblelight image and a fluorescence image on each other.

Solution to Problem

According to an embodiment of the present disclosure, there is providedmedical imaging device including a color separation prism that has adichroic film configured to split light into first light belonging to avisible light wavelength band and second light belonging to afluorescence wavelength band, a fluorescence image sensor that isprovided at an output side of the color separation prism and that isconfigured to image at least part of the second light belonging to thefluorescence wavelength band separated by the dichroic film, a visiblelight image sensor that is provided at the output side of the colorseparation prism and that is configured to image at least part of thefirst light belonging to the visible light wavelength band separated bythe dichroic film, and a bandpass filter that is disposed between thecolor separation prism and the fluorescence image sensor. Thefluorescence image sensor and the visible light image sensor arearranged such that an optical path difference between an optical pathlength of a fluorescence optical path for the second light imaged on thefluorescence image sensor via the color separation prism and an opticalpath length of a visible light optical path for the first light imagedon the visible light image sensor via the color separation prismcorresponds to an amount of a shift between a fluorescence imagingposition and a visible light imaging position, the shift being generatedby an imaging lens positioned at an input side of the color separationprism. The fluorescence imaging position is an imaging position offiltered second light, which results from passing the second lightthrough the bandpass filter, such that the amount of shift is based onthe filtered second light.

According to an embodiment of the present disclosure, there is provideda medical microscopic system including a microscopic optical lensassembly including at least an objective lens and an imaging lens, andan imaging device configured to capture a magnified image of an object.The imaging device includes a color separation prism that has a dichroicfilm configured to split light into first light belonging to the visiblelight wavelength band and second light belonging to the fluorescencewavelength band, a fluorescence image sensor that is provided at anoutput side of the color separation prism and that is configured toimage at least part of the second light belonging to the fluorescencewavelength band separated by the dichroic film, a visible light imagesensor that is provided at the output side of the color separation prismand that is configured to image at least part of the first lightbelonging to the visible light wavelength band separated by the dichroicfilm, and a bandpass filter that is disposed between the colorseparation prism and the fluorescence image sensor. The fluorescenceimage sensor and the visible light image sensor are arranged such thatan optical path difference between an optical path length of afluorescence optical path for the second light imaged on thefluorescence image sensor via the color separation prism and an opticalpath length of a visible light optical path for the first light imagedon the visible light image sensor via the color separation prismcorresponds to an amount of a shift between a fluorescence imagingposition and a visible light imaging position, the shift being generatedby an imaging lens positioned at an input side of the color separationprism. The fluorescence imaging position is an imaging position offiltered second light, which results from passing the second lightthrough the bandpass filter, such that the amount of shift is based onthe filtered second light.

According to an embodiment of the present disclosure, there is providedan endoscopic system including an endoscopic optical lens assembly, animaging device configured to capture an image of an object, and ancoupler optical lens assembly that is provided between the endoscopicoptical lens assembly and the imaging device. The imaging deviceincludes a color separation prism that has a dichroic film configured tosplit light into first light belonging to the visible light wavelengthband and second light belonging to the fluorescence wavelength band, afluorescence image sensor that is provided at an output side of thecolor separation prism and that is configured to image at least part ofthe second light belonging to the fluorescence wavelength band separatedby the dichroic film, a visible light image sensor that is provided atthe output side of the color separation prism and that is configured toimage at least part of the first light belonging to the visible lightwavelength band separated by the dichroic film, and a bandpass filterthat is disposed between the color separation prism and the fluorescenceimage sensor. The fluorescence image sensor and the visible light imagesensor are arranged such that an optical path difference between anoptical path length of a fluorescence optical path for the second lightimaged on the fluorescence image sensor via the color separation prismand an optical path length of a visible light optical path for the firstlight imaged on the visible light image sensor via the color separationprism corresponds to an amount of a shift between a fluorescence imagingposition and a visible light imaging position, the shift being generatedby an imaging lens positioned at an input side of the color separationprism. The fluorescence imaging position is an imaging position offiltered second light, which results from passing the second lightthrough the bandpass filter, such that the amount of shift is based onthe filtered second light.

Accordingly in the present embodiments, axial chromatic aberrationcontained in fluorescence imaged by the fluorescence image sensor iscompletely corrected by setting arrangement positions of thefluorescence image sensor and the visible light image sensor asdescribed above.

Advantageous Effects of Invention

As described above, according to an embodiment of the presentdisclosure, it is possible to split light from an observation targetinto a visible light component and a fluorescence component with highaccuracy and to obtain a favorable superimposed image by superimposing avisible light image and a fluorescence image on each other.

Note that the effects described above are not necessarily limited, andalong with or instead of the effects, any effect that is desired to beintroduced in the present specification or other effects that can beexpected from the present specification may be exhibited.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is an explanatory diagram schematically illustrating an exampleof a configuration of an image pickup device according to an embodimentof the present disclosure.

FIG. 1B is an explanatory diagram schematically illustrating an exampleof the configuration of the image pickup device according to theembodiment.

FIG. 2 is a graph showing an example of a spectral transmittancecharacteristic of a dichroic film provided in the image pickup deviceaccording to the embodiment.

FIG. 3 is a graph showing an example of a spectral transmittancecharacteristic of a bandpass filter provided in the image pickup deviceaccording to the embodiment.

FIG. 4 is an explanatory diagram schematically illustrating an exampleof a configuration of a 2-piece camera system including the image pickupdevice according to the embodiment.

FIG. 5 is a block diagram showing an example of a configuration of acamera control unit that can be used for the image pickup deviceaccording to the embodiment.

FIG. 6 is an explanatory diagram schematically illustrating an exampleof a configuration of a microscope image pickup system including theimage pickup device according to the embodiment.

FIG. 7A is an explanatory diagram schematically illustrating anotherexample of the configuration of the image pickup device according to theembodiment.

FIG. 7B is an explanatory diagram schematically illustrating anotherexample of the configuration of the image pickup device according to theembodiment.

FIG. 8 is an explanatory diagram schematically illustrating an exampleof a configuration of an endoscope image pickup system including theimage pickup device according to the embodiment.

FIG. 9 is a block diagram showing an example of a hardware configurationof the camera control unit that can be used for the image pickup deviceaccording to the embodiment.

DESCRIPTION OF EMBODIMENTS

Hereinafter, (a) preferred embodiment(s) of the present disclosure willbe described in detail with reference to the appended drawings. In thisspecification and the appended drawings, structural elements that havesubstantially the same function and structure are denoted with the samereference numerals, and repeated explanation of these structuralelements is omitted.

Note that the following description is given in the order indicatedbelow.

-   -   1. Study by Inventor of the Present Disclosure    -   2. First Embodiment    -   2.1 Example of Configuration of Image Pickup Device    -   2.2 2-piece Camera System Including Image Pickup Device    -   2.3 Configuration of Camera Control Unit That Can Be Used for        Image Pickup Device    -   2.4 Microscope Image Pickup System Including Image Pickup Device    -   2.5 Another Example of Configuration of Image Pickup Device    -   2.6 Endoscope Image Pickup System Including Image Pickup Device    -   3. Hardware Configuration of Camera Control Unit

(Study by Inventor of the Present Disclosure)

Prior to description of an image pickup device, a microscope imagepickup system, and an endoscope image pickup system according to anembodiment of the present disclosure, the content of study performed bythe inventor of the present disclosure regarding an image pickup systemfor performing superimposed display of a fluorescence image and avisible light image in real time will be briefly described, and what theembodiment of the present disclosure aims at will be briefly described.

Prior to study of the image pickup device according to the embodiment ofthe present disclosure, the inventor of the present disclosure firststudied a technology disclosed in PTL 1 cited above. As a result, theinventor found that it was important to further study the technologydisclosed in PTL 1 cited above regarding the following points. That is,in PTL 1 cited above, only a fluorescence component is attempted to beextracted from an incident observed luminous flux by using only anoptical multilayer film having a characteristic that “the branch opticalmechanism is an optical block having an interface for coaxiallyseparating only fluorescence having a predetermined wavelength fromvisible light in the observed luminous flux”. However, the inventor ofthe present disclosure found that there were problems described below inorder to extract only the fluorescence component.

First, in PTL 1 cited above, the above optical block functioning as thebranch optical mechanism is attempted to be achieved by adhering twoprisms to each other and providing the optical multilayer film havingthe above characteristic between adhered surfaces. At this time, inorder to split an optical path into an optical path of visible light andan optical path of near-infrared fluorescence, the adhered surfaces ofthe prisms (in other words, an interface between the two prisms) of theoptical block are inclined with respect to an optical axis, and an angleof incidence of beams of light to the interface is increased.

Herein, it is known that the characteristic of the optical multilayerfilm is changed in accordance with an angle of incidence of beams oflight to be incident thereon. That is, a spectral characteristic of theoptical multilayer film is originally designed assuming that beams oflight are vertically incident on the multilayer film. However, asdescribed in PTL 1 cited above, in the case where an angle of incidenceof beams of light is increased, and, as a result, the beams of the lightare not vertically incident on the optical multilayer film, it isimportant to increase the number of optical thin films included in theoptical multilayer film in order to achieve the same spectralcharacteristic as a spectral characteristic obtained when beams of lightare vertically incident thereon. As a result, it is difficult to reducea size of an optical prism and costs are increased. In the case wherebeams of light having a bright f-number are incident on the opticalprism disclosed in PTL 1 cited above, a change in spectralcharacteristic caused by a difference in angle of incidence betweenupper beams of light and lower beams of light is not suppressed. Thus, adesired spectral characteristic is not achieved.

That is, in the technology disclosed in PTL 1 cited above, the followingmatter for study exists: the characteristic of the optical multilayerfilm for dividing beams of light into two parts, the number of arrangedoptical multilayer films, and a positional rela-tionship with theoptical multilayer film are not preferable.

It can also be considered that axial chromatic aberration is greatlygenerated in a fluorescence wavelength band depending on a spectralcharacteristic of a fluorescence image to be focused on. Regarding thispoint, the technology disclosed in PTL 2 cited above attempts to correctaxial chromatic aberration by disposing the monochrome image sensor sothat the monochrome image sensor is isolated from the beam splitter at adistance Δ, as compared with the color image sensor. However, as aresult of study performed by the inventor of the present disclosure, itis found that, even in the case where a difference in the center ofchromatic aberration between a visible light wavelength band and thefluorescence wavelength band is corrected by providing the isolationdistance Δ, components of wavelengths other than a central wavelength inthe fluorescence wavelength band form a blur image and a contrast isreduced. That is, it is found that the effect of the isolation distanceΔ is not satisfactorily exerted in some cases in the technologydisclosed in PTL 2 cited above. Because PTL 2 cited above neitherdiscloses a condition that is necessary for a spectral characteristic ofan optical filter nor a method of achieving the isolation distance Δ,PTL 2 cited above discloses no method of completely correcting axialchromatic aberration. Therefore, the method of completely correctingaxial chromatic aberration is a matter for study.

The inventor of the present disclosure found the above matters for studyand then focused on an image pickup system capable of performingsuperimposed display of a visible light image and a fluorescence imagein real time. Such an image pickup system can be achieved by using animage pickup device capable of separating a visible light image and afluorescence image with high accuracy and a control unit that controlsthe image pickup device.

An example of the image pickup system is a medical CMOS full HD videocamera including a camera head unit (CHU) and a camera control unit(CCU) (Hereinafter, such an image pickup system including a CHU and aCCU will be also referred to as “2-piece camera”.). In the image pickupsystem, the CHU includes a single-plate image pickup element having anRGB color filter or a 3-color separation prism module, and a user cancapture a full-HD image with high color reproducibility by attaching anarbitrary imaging lens (various kinds of optical systems such as amicroscope and an endoscope) to the CHU.

An example of the similar image pickup system is a CHU for a rigidendoscope. The CHU for a rigid endoscope includes a coupler opticalsystem, and an eyepiece unit of the rigid endoscope is detachable fromthe CHU. In the CHU, the coupler optical system images a substantiallyafocal luminous flux from the eyepiece unit on an image pickup element.

In the above image pickup system, depending on an optical system(imaging lens or rigid endoscope) to be used by a user, axial chromaticaberration is generated between the visible light wavelength band andthe fluorescence wavelength band, and imaging positions thereof aredifferent in an optical axis direction. As a result, when a visiblelight image is focused in the CHU, a fluorescence image is not focused,whereas, when the fluorescence image is focused, the visible light imageis not focused. That is, both the images are not simultaneously capturedwith the best pint. Therefore, in related arts, observation is performedon an average image surface while a balance is being kept betweenvisible light and fluorescence. In particular, even in the case wherethe optical system to be used by the user has an MTF of full-HDresolution, the CHU does not satisfactorily exert resolution performancewhen the CHU has the matters for study in the technologies disclosed inPTL 1 and PTL 2 cited above.

In view of this, the inventor of the present disclosure has diligentlystudied to solve the above matters for study and achieve an image pickupdevice (CHU) capable of splitting light into visible light andfluorescence with high accuracy even in the case where a user uses anarbitrary optical system. As a result, the inventor has arrived at amethod of solving the above matters for study and have arrived at animage pickup device capable of splitting light into visible light andfluorescence with high accuracy. When the image pickup device is used,it is possible to superimpose visible light and fluorescence in a statein which both the visible light and the fluorescence are focused.Therefore, it is possible to achieve an image pickup system capable ofgenerating a better superimposed image.

Hereinafter, the image pickup device that has been completed as a resultof diligent study by the inventor of the present disclosure and amicroscope image pickup system and an endoscope image pickup system eachof which includes the image pickup device will be described in detail.

First Embodiment

Hereinafter, an image pickup device, a microscope image pickup system,and an endoscope image pickup system according to a first embodiment ofthe present disclosure will be described in detail with reference to thedrawings.

Note that, hereinafter, there will be described an example wherefluorescence having a wavelength of 832 nm belonging to a near-infraredband, the fluorescence being emitted from indocyanine green (excitationwavelength: about 769 nm), is focused on. However, even in the casewhere fluorescence belonging to another wavelength band is focused on,it is possible to similarly apply a technical idea of an embodiment ofthe present disclosure by changing spectral characteristics of adichroic film and a bandpass filter described below to spectralcharacteristics thereof suitable for fluorescence to be focused on.

<Example of Configuration of Image Pickup Device>

An example of a configuration of an image pickup device according to theembodiment will be described in detail with reference to FIG. 1A to FIG.3. FIG. 1A and FIG. 1B are explanatory diagrams each of whichschematically illustrates an example of the configuration of the imagepickup device according to the embodiment. FIG. 2 is a graph showing anexample of a spectral transmittance characteristic of a dichroic filmprovided in the image pickup device according to the embodiment. FIG. 3is a graph showing an example of a spectral transmittance characteristicof a bandpass filter provided in the image pickup device according tothe embodiment.

In the case where incident light containing both light belonging to thevisible light wavelength band and light belonging to the fluorescencewavelength band is incident on the image pickup device according to theembodiment, the image pickup device splits the incident light into thelight belonging to the visible light wavelength band and the lightbelonging to the fluorescence wavelength band with high accuracy andthen independently captures images of the light belonging to therespective wavelength bands to generate a visible light captured image(hereinafter, also simply referred to as “visible light image”) and afluorescence captured image (hereinafter, also simply referred to as“fluorescence image”).

As schematically illustrated in, for example, FIG. 1A, such an imagepickup device 10 includes at least a color separation prism 101, avisible light image pickup element 111, a bandpass filter 115, and afluorescence image pickup element 117.

The color separation prism 101 is an optical member that splits incidentlight incident on the image pickup device 10 into light belonging to thevisible light wavelength band and light belonging to the fluorescencewavelength band. The color separation prism 101 includes a dichroic film103 for splitting light into light belonging to the visible lightwavelength band and light belonging to the fluorescence wavelength band.

The dichroic film 103 is an optical film that splits incident lightincident on the color separation prism 101, the incident lightcontaining light belonging to the visible light wavelength band andlight belonging to the fluorescence wavelength band, into the lightbelonging to the visible light wavelength band and the light belongingto the fluorescence wavelength band. FIG. 2 shows an example of aspectral transmittance characteristic of the dichroic film 103 accordingto the embodiment. In FIG. 2, a horizontal axis indicates a wavelengthof light (unit: nm) incident on the dichroic film 103, whereas avertical axis indicates spectral transmittance (unit: %).

In the case where fluorescence having a wavelength of 832 nm belongingto the near-infrared band, the fluorescence being emitted fromindocyanine green, is focused on, as shown in FIG. 2, the spectraltransmittance of the dichroic film 103 preferably has a characteristicthat reflects light in the visible light wavelength band and allowslight in a near-infrared wavelength band to transmit therethrough. Morespecifically, as shown in FIG. 2, the dichroic film 103 preferably hastransmittance of 90% or more in a wavelength band from 780 nm to 880 nmand transmittance of 10% or less in a wavelength band from 400 nm to 720nm.

The transmittance of less than 90% in the wavelength band from 780 nm to880 nm is not preferable because a ratio of fluorescence that is nottransmitted through the dichroic film 103 is increased and brightness ofa fluorescence image is reduced. Such a case is also not preferable interms of image quality of a visible light image because fluorescenceleaks into the visible light image pickup element 111 to thereby reducea contrast of the visible light image.

The transmittance exceeding 10% in the wavelength band from 400 nm to720 nm is not preferable because a ratio of visible light that is notreflected by the dichroic film 103 but is transmitted therethrough isincreased and brightness of a visible light image is reduced. Such acase is also not preferable in terms of image quality of a fluorescenceimage because visible light leaks into the fluorescence image pickupelement 117 to thereby reduce a contrast of the fluorescence image.

As is clear from FIG. 2 and the above description, the dichroic film 103according to the embodiment splits incident light into two colors, i.e.,light belonging to a predetermined fluorescence wavelength band and aband of longer wavelengths than the predetermined fluorescencewavelength band and light belonging to a band of shorter wavelengthsthan the predetermined fluorescence wavelength band. More specifically,the dichroic film 103 having the characteristic shown in FIG. 2 is afilm functioning like a low-pass filter that splits incident light intotwo groups by setting a boundary to 750 nm which is a boundary betweenthe visible light wavelength band and the fluorescence wavelength band.

Accordingly, the spectral characteristic of the dichroic film 103according to the embodiment is comparatively broad as shown in FIG. 2,and, in the case where the dichroic film 103 is achieved as an opticalmultilayer film, the number of layers of the film can be reduced toabout several tens of layers and a general vacuum deposition method canbe used as a manufacturing method thereof. In the optical multilayerfilm disclosed in PTL 1 cited above, it is necessary to have anextraordinarily large number of layers of the film to achieve a functionof extracting only fluorescence that is focused on by using only theoptical multilayer film. Instead of extracting only fluorescence that isfocused on by using only the dichroic film 103, the dichroic film 103according to the embodiment only separates light in a long-wavelengthband containing fluorescence that is focused on from incident light.Therefore, it is possible to obtain an optical multilayer film that isless expensive and more accurate than the optical multilayer filmdisclosed in PTL 1 cited above.

Note that the image pickup device 10 according to the embodimentincludes the bandpass filter 115 described below in order to extractfluorescence that is focused on from light in the long-wavelength bandcontaining fluorescence, the light having been separated by the dichroicfilm 103. When the bandpass filter 115 is used, light other thanfluorescence is removed from light to be imaged on the fluorescenceimage pickup element 117, and a contrast of a fluorescence image istherefore improved.

A structure of the color separation prism 101 having the dichroic film103 is not limited, and, in particular, the structure may have anarbitrary shape in the case where a size of the whole image pickupdevice 10 is not limited. However, in the case where the image pickupdevice 10 according to the embodiment is attached to various kinds ofoptical systems described above, such as a microscope and an endoscope,and functions as a camera head unit (CHU), the size of the image pickupdevice 10 is preferably reduced as much as possible. In order to reducethe size of the image pickup device 10, the color separation prism 101preferably has a structure illustrated in FIG. 1A.

For example, the color separation prism 101 illustrated in FIG. 1A is aprism obtained by joining a first prism 105 and a second prism 107 toeach other, and the first prism 105 and the second prism 107 are joinedto each other via the dichroic film 103. That is, the dichroic film 103is provided on an interface between the first prism 105 and the secondprism 107.

Light belonging to the visible light wavelength band and light belongingto the fluorescence wavelength band (that is, incident light) areincident on the first prism 105, and the first prism 105 functions as avisible light optical path through which the light belonging to thevisible light wavelength band is guided. The second prism 107 functionsas a fluorescence optical path through which the light belonging to thefluorescence wavelength band is guided.

The incident light incident on the first prism 105 moves straight in thefirst prism 105 and is split by the dichroic film 103 that is obliquelyprovided on the optical axis into the light belonging to the visiblelight wavelength band and the light belonging to the fluorescencewavelength band.

The light belonging to the visible light wavelength band is reflected bythe dichroic film 103 to be guided in the first prism 105. Herein, thereflected and split light belonging to the visible light wavelength band(that is, visible light rays) is totally reflected at a position Aillustrated in FIG. 1A only once and is transmitted to the outside ofthe first prism 105. With this, an angle formed by a film depositionsurface of the dichroic film 103 and the optical axis can be close to aright angle. Conversely, an installation angle of the dichroic film 103according to the embodiment on the optical axis is set to satisfy atotal reflection condition of visible light rays at the position A.Because the dichroic film 103 is disposed as described above, it ispossible to suppress a change in spectral characteristic of the dichroicfilm 103 caused by a difference in angle of incidence between upperbeams of light and lower beams of light even in the case where beams oflight having a bright f-number are incident on the first prism 105.Therefore, it is possible to split wavelengths with high accuracy.

The visible light rays transmitted through the first prism 105 areguided to the visible light image pickup element 111. At this time, aninfrared cut-off filter 113 may be provided between an emission surfaceof the first prism 105 and the visible light image pickup element 111.When the infrared cut-off filter 113 is provided, it is possible toremove infrared light contained in the visible light rays transmittedthrough the first prism 105, and therefore color reproducibility of avisible light image can be further improved. As the infrared cut-offfilter 113, for example, a publicly-known absorption filter such asC5000 manufactured by HOYA CORPORATION can be used.

Meanwhile, the light belonging to the fluorescence wavelength bandtransmitted through the dichroic film 103 is incident on the secondprism 107 and moves straight in the second prism 107. An end surface ofthe second prism 107, which is opposite to an end surface on which thedichroic film 103 is provided (in other words, an emission surface ofthe second prism 107 on a downstream side of the optical axis), isprovided to be vertical to the optical axis, and the light belonging tothe fluorescence wavelength band is transmitted to the outside of thesecond prism 107 while being vertical to the emission surface of thesecond prism 107.

The light belonging to the fluorescence wavelength band, which has beentransmitted through the second prism 107, is incident on the bandpassfilter 115 provided at a latter stage.

Heretofore, the color separation prism 101 according to the embodimenthas been described in detail. Note that a material of the colorseparation prism 101 according to the embodiment is not particularlylimited, and publicly-known optical glass or optical crystal can be usedas appropriate in accordance with a wavelength of light to be guided inthe color separation prism 101.

The color separation prism 101 according to the embodiment can bemanufactured by cutting shapes of the first prism 105 and the secondprism 107 from publicly-known optical glass or optical crystal andforming the dichroic film 103 between joining surfaces of the firstprism 105 and the second prism 107 by a publicly-known method such as avacuum deposition method. At this time, needless to say, the dichroicfilm 103 may be formed on the first prism 105 side, or the dichroic film103 may be formed on the second prism 107.

The visible light image pickup element 111 will be described.

The visible light image pickup element 111 is provided at a latter stageof the color separation prism 101 (more specifically, at a latter stageof the first prism 105) and is an image pickup element on which lightbelonging to the visible light wavelength band separated by the dichroicfilm 103 is imaged. When the light belonging to the visible lightwavelength band is imaged on the visible light image pickup element 111,a visible light image is generated. Herein, in the case where afluorescence image described below and the visible light image aresuperimposed, it is preferable that, in order to position both theimages more easily, the visible light image pickup element 111 bedisposed so that an optical axis of visible light rays emitted from thefirst prism 105 is imaged on the center of the visible light imagepickup element 111.

The visible light image pickup element 111 is preferably a single-plateimage pickup element having an RGB color filter such as a CCD or a CMOS.

Note that, in the case where a 3-color separation prism is disposed at alatter stage of the first prism 105 to split the visible light raysemitted from the first prism 105 into three colors of an R component, aG component, and a B component, the visible light image pickup element111 can be formed to have a three-plate configuration. With thisconfiguration, it is possible to further improve the colorreproducibility of a visible light image and therefore to implementimage capturing processing with higher sen-sitivity.

The bandpass filter 115 will be described.

The bandpass filter 115 according to the embodiment is disposed betweenthe color separation prism 101 (more specifically, the second prism 107)and the fluorescence image pickup element 117 and has a plane ofincidence vertical to the optical axis. The bandpass filter 115 canextract only fluorescence that is focused on from light belonging to thefluorescence wavelength band separated by the dichroic film 103.

The bandpass filter 115 according to the embodiment has a bandpasscharacteristic that reflects light other than light in the fluorescencewavelength band and allows only the light in the fluorescence wavelengthband to transmit therethrough. FIG. 3 shows an example of a spectraltransmittance characteristic of the bandpass filter 115 according to theembodiment. In FIG. 3, a horizontal axis indicates a wavelength (unit:nm) of light incident on the bandpass filter 115, whereas a verticalaxis indicates spectral transmittance (unit: %).

In the case where fluorescence having a wavelength of 832 nm belongingto the near-infrared band, the fluorescence being emitted fromindocyanine green, is focused on, as shown in FIG. 3, the spectraltransmittance of the bandpass filter 115 is preferably 90% or more in awavelength band from 820 nm to 850 nm and is preferably 10% or less in awavelength band from 400 nm to 805 nm and in a wavelength band from 860nm to 1000 nm.

The transmittance of less than 90% in the wavelength band from 820 nm to850 nm is not preferable because a ratio of fluorescence transmittedthrough the bandpass filter 115 is reduced and brightness of afluorescence image is reduced. The transmittance exceeding 10% in thewavelength band from 400 nm to 805 nm and in the wavelength band from860 nm to 1000 nm is not preferable because light from the outside otherthan fluorescence, such as excitation light having a wavelength of about800 nm, is imaged on the fluorescence image pickup element 117 tothereby remarkably reduce a contrast of the fluorescence image.

In the case where a wavelength band of light transmitted through thebandpass filter 115 is extremely wider than the wavelength band from 820nm to 850 nm, a near-infrared wavelength band contributing to formationof the fluorescence image is extremely wide. As a result, even in thecase where the center of axial chromatic aberration can be corrected bythe isolation distance Δ described below, a component having a longerwavelength forms a blur image and a contrast is reduced. This is notpreferable.

In the case where a wavelength band of light transmitted through thebandpass filter 115 is extremely narrower than the wavelength band from820 nm to 850 nm, the light transmitted through the bandpass filter 115is close to one color and an effect of correcting axial chromaticaberration by using the isolation distance Δ described below isimproved, but brightness of the fluorescence image is reduced. This isnot preferable.

The bandpass filter 115 according to the embodiment can be manufacturedby using a publicly-known optical material in accordance with awavelength of fluorescence to be focused on. For example, the bandpassfilter 115 according to the embodiment may be manufactured by depositingan optical multilayer film on a glass substrate corre-sponding to BK7 ormay be manufactured by using visible absorption glass as a substrate,such as R80 manufactured by HOYA CORPORATION, and depositing an opticalmultilayer film on the substrate. With this, it is possible to suppresstransmittance in a visible light region in a configuration including aglass substrate and to contribute to improvement in contrast of thefluorescence image.

Note that, although the bandpass filter 115 according to the embodimentcan be deposited by a vacuum deposition method in the same way as thedichroic film 103, a spectral characteristic thereof is a narrow bandand has a steep rise/fall shape, and therefore the number of layers ofthe film is greater than the number of layers of the dichroic film 103,i.e., is about several hundreds of layers. Thus, a deposition methodthat can secure high reliability, such as an ion beam sputtering method,is preferably employed instead of the vacuum deposition method.

Because the bandpass filter 115 according to the embodiment is disposedbetween the color separation prism 101 and the fluorescence image pickupelement 117 and has a plane of incidence vertical to the optical axis,it is possible to suppress a change in spectral characteristic caused bya difference in angle of incidence between upper beams of light andlower beams of light even in the case where beams of light having abright f-number are incident.

It is also considered that, in the case where the bandpass filter 115 ismanufactured, the substrate is warped at the time of deposition. Whensuch a warped component is incorporated into an image pickup system,resolution is reduced. Therefore, it is preferable to deposit bandpassfilms on both surfaces of the substrate because warpage on both thesurfaces can be offset.

Although the emission surface of the second prism 107 and the bandpassfilter 115 are isolated in FIG. 1A, the bandpass filter 115 may bejoined to the emission surface of the second prism 107. Thisconfiguration is more preferable because a contact surface with air isreduced and therefore a risk of ghost flare can be reduced. Instead ofseparately forming the second prism 107 and the bandpass filter 115, abandpass film may be deposited on the emission surface of the secondprism 107. With this configuration, it is possible not only to reducethe above risk of ghost flare but also to remove a filter substrate.Therefore, further reduction in size and weight can be achieved.

The fluorescence image pickup element 117 will be described.

The fluorescence image pickup element 117 is provided at a latter stageof the bandpass filter 115 and is an image pickup element on whichfluorescence extracted by the bandpass filter 115 is imaged. When thefluorescence extracted by the bandpass filter 115 is imaged on thefluorescence image pickup element 117, a fluorescence image isgenerated.

Herein, it is preferable to determine a fixed position of thefluorescence image pickup element 117 while shifting and adjusting theimage pickup element 117 in a direction vertical to the optical axis soas to minimize an image shift of a fluorescence image from a visiblelight image generated by the visible light image pickup element 111.With this, in the case where a fluorescence image and a visible lightimage are superimposed, both the images can be positioned more easily.Note that, instead of the above adjustment of the position, thefollowing method may be used: a fixed position of the fluorescence imagepickup element 117 is determined and then a magnitude of an image shiftof a fluorescence image from a visible light image, which is caused bytolerance of components, is specified; and a reading start position of afluorescence image signal is shifted so as to minimize the magnitude ofthe specified image shift. When the method of adjusting the readingstart position is used, the above adjustment processing can be omitted.This is advantageous in terms of costs.

The fluorescence image pickup element 117 may be a single-plate imagepickup element having an RGB color filter such as a CCD or a CMOS.

The isolation distance Δ between the bandpass filter 115 and thefluorescence image pickup element 117 in the image pickup device 10according to the embodiment will be described.

In the case where the image pickup device 10 according to the embodimentis actually used, a publicly-known imaging lens is attached at a formerstage of the image pickup device 10 (more specifically, at a formerstage of the color separation prism 101), and visible light rays andfluorescence are imaged on the respective image pickup elements. At thistime, an imaging position of visible light rays and an imaging positionof fluorescence are different due to axial chromatic aberration of theimaging lens, and, in the image pickup device 10 according to theembodiment, a shift between the imaging positions caused by this axialchromatic aberration is completely corrected by setting the isolationdistance Δ illustrated in FIG. 1A.

That is, in the image pickup device 10 according to the embodiment, thefluorescence image pickup element 117 and the visible light image pickupelement 111 are arranged so that an optical path difference Δd betweenan optical path length of the fluorescence optical path imaged on thefluorescence image pickup element 117 via the color separation prism 101and an optical path length of the visible light optical path imaged onthe visible light image pickup element 111 via the color separationprism 101 corresponds to an amount of a shift between a fluorescenceimaging position and a visible light imaging position (that is, amagnitude of the axial chromatic aberration), the shift being generatedby the imaging lens attached at the former stage of the color separationprism 101. Specifically, the position of the fluorescence image pickupelement 117 is controlled so that the isolation distance Δ illustratedin FIG. 1A is changed to be the optical path difference Δd.

Herein, the magnitude of the axial chromatic aberration caused by theimaging lens is changed in accordance with a configuration of an opticalsystem of the imaging lens or the like and is different for each imaginglens. Therefore, in the case where the imaging lens attached at theformer stage of the color separation prism 101 is not uniquelydetermined, it is important to control the isolation distance Δ inaccordance with the imaging lens. In view of this, in such a case, theisolation distance Δ is set to be changeable and a fluorescence imagefocusing mechanism 119 is provided in the image pickup device 10 asschematically illustrated in FIG. 1A to control a length of theisolation distance Δ.

As the fluorescence image focusing mechanism 119, for example, anactuator such as a stepping motor or a piezoelectric element can beused, or a cam mechanism or the like can also be used.

When any one of an optical unit 11 including the color separation prism101, the visible light image pickup element 111, and the bandpass filter115 and the fluorescence image pickup element 117 is moved along theoptical axis by the fluorescence image focusing mechanism 119, thelength of the isolation distance Δ can be controlled. At this time, thefluorescence image focusing mechanism 119 may move the position of thefluorescence image pickup element 117 along the optical axis after aposition of the whole optical unit 11 is fixed, or the fluorescenceimage focusing mechanism 119 may move the position of the whole opticalunit 11 along the optical axis after the position of the fluorescenceimage pickup element 117 is fixed.

A focusing method using the fluorescence image focusing mechanism 119will be briefly described.

Publicly-known imaging lenses that are sold by various companies and areattachable to the image pickup device 10 according to the embodimenthave a focusing mechanism. When the focusing mechanism is used, avisible light image can be focused (that is, visible light rays can befocused on the visible light image pickup element 111). At this time, inthe imaging lens, axial chromatic aberration is generally corrected onlyin the visible light wavelength band, and therefore axial chromaticaberration in the near-infrared fluorescence wavelength band is notcorrected in many cases. In the case where only the visible light imageis focused, a fluorescence image is blurred. In view of this, thefluorescence image focusing mechanism 119 described above adjustsrelative positions of the optical unit 11 and the fluorescence imagepickup element 117, thereby focusing the fluorescence image. With this,it is possible to focus the fluorescence image while the visible lightimage is in a focused state.

In the case where the kind of the imaging lens to be used by a user isuniquely determined, the following method may be used, instead ofproviding the fluorescence image focusing mechanism 119 in the imagepickup device 10. That is, as illustrated in FIG. 1B, after themagnitude Δd of the axial chromatic aberration of the imaging lensbetween visible light rays and fluorescence is measured, a fixationadhesion position of the fluorescence image pickup element 117 may beoffset by Δd.

Note that a configuration and a method for changing the above isolationdistance Δ are not particularly limited.

Heretofore, the image pickup device 10 according to the embodiment hasbeen described in detail with reference to FIG. 1A to FIG. 3.

Note that, in the image pickup device 10 according to the embodiment, itis also possible to achieve an optical configuration in which thepositions of the visible light image pickup element 111 and thefluorescence image pickup element 117 are switched. In this case, it isnecessary to form the dichroic film 103 so that light in the visiblelight wavelength band is allowed to transmit therethrough and light inthe fluorescence wavelength band is reflected. It is also necessary todispose the bandpass filter 115 at a latter stage of the first prism105.

A light source for observing a measurement target object (for example,an affected part on which a fluorescent probe is accumulated) withvisible light is not particularly limited, and it is possible to use axenon lamp which is a general white light source. In this case, aradiation spectrum includes both an excitation wavelength of thefluorescent probe and the visible light wavelength band, and thereforeit is only necessary to prepare a single light source, which isadvantageous. However, the radiation spectrum of the xenon lamp alsoincludes the fluorescence wavelength band, and therefore a component inthe fluorescence wavelength band of the xenon lamp is imaged on thefluorescence image pickup element 117, thereby reducing a fluorescencecontrast. Thus, in the case where the xenon lamp is used, in order toprevent such reduction in contrast, a filter having a spectraltransmittance characteristic that blocks the fluorescence band ispreferably disposed in a light source.

<2-Piece Camera System Including Image Pickup Device>

An example of a 2-piece camera system including the image pickup device10 according to the embodiment will be described with reference to FIG.4. FIG. 4 is an explanatory diagram schematically illustrating anexample of a configuration of a 2-piece camera system including theimage pickup device according to the embodiment.

The 2-piece camera system described above can be achieved by using theimage pickup device 10 according to the embodiment described above. Asillustrated in FIG. 4, the 2-piece camera system includes the imagepickup device 10 according to the embodiment and a camera control unit(CCU) 30.

Herein, a publicly-known imaging lens 20 is attached to the image pickupdevice 10, and both a visible light image and a fluorescence image arein a focused state by a focusing function of the imaging lens 20 andcontrol of the isolation distance Δ in the image pickup device 10according to the embodiment.

The image pickup device 10 independently generates a visible light imageand a fluorescence image under image capturing control of the cameracontrol unit 30 described below and outputs data of the generatedcaptured images to the camera control unit 30.

The camera control unit 30 controls image capturing processing of theimage pickup device 10 and superimposes the visible light image and thefluorescence image generated by the image pickup device 10 to generate asuperimposed image. The camera control unit 30 can be achieved by any ofvarious kinds of computers including a central processing unit (CPU), aread only memory (ROM), a random access memory (RAM), and the like. Notethat an example of a detailed configuration of the camera control unit30 will be described below.

The superimposed image generated by the camera control unit 30 isdisplayed as necessary on a display device 40 such as a display providedin the camera control unit 30 or the display device 40 such as a displayprovided outside the camera control unit 30. With this, a user of the2-piece camera system can instantly grasp the superimposed image inwhich the visible light image and the fluorescence image aresuperimposed with satisfactory resolution.

Heretofore, an example of the configuration of the 2-piece camera systemincluding the image pickup device 10 according to the embodiment hasbeen briefly described with reference to FIG. 4.

<Configuration of Camera Control Unit that can be Used for Image PickupDevice>

An example of a configuration of the camera control unit 30 that can beused for the image pickup device 10 according to the embodiment will bebriefly described with reference to FIG. 5. FIG. 5 is a block diagramshowing an example of a configuration of a camera control unit that canbe used for the image pickup device according to the embodiment.

As schematically illustrated in FIG. 5, the camera control unit 30 thatcan be used for the image pickup device 10 according to the embodimentmainly includes an image pickup device control unit 301, an image dataacquisition unit 303, a superimposed image generation unit 305, asuperimposed image output unit 307, a display control unit 309, and astorage unit 311.

The image pickup device control unit 301 is realized by, for example, aCPU, a ROM, a RAM, and a communication device. The image pickup devicecontrol unit 301 comprehensively controls the whole image capturingprocessing implemented in the image pickup device 10 according to theembodiment. In the case where the fluorescence image focusing mechanism119 is provided in the image pickup device 10 according to theembodiment, the image pickup device control unit 301 also controls thefluorescence image focusing mechanism 119.

The image pickup device 10 according to the embodiment generates avisible light image and a fluorescence image at predetermined timeintervals under the control of the image pickup device control unit 301and outputs the generated images to the camera control unit 30 asnecessary.

The image data acquisition unit 303 is realized by, for example, a CPU,a ROM, a RAM, and a communication device. The image data acquisitionunit 303 acquires data of the visible light image and data of thefluorescence image output from the image pickup device 10 as necessaryand outputs the data to the superimposed image generation unit 305described below. The image data acquisition unit 303 may associate theacquired image data with a timestamp of date and time at which the imagedata has been acquired and store the image data associated with thetimestamp as history information in the storage unit 311 describedbelow.

The superimposed image generation unit 305 is realized by, for example,a CPU, a ROM, and a RAM. By using the visible light image and thefluorescence image output from the image data acquisition unit 303, thesuperimposed image generation unit 305 implements superimposingprocessing of the visible light image and the fluorescence image whilepositioning the visible light image and the fluorescence image, therebygenerating a superimposed image in which those images are superimposedon each other. Note that processing for generating a superimposed image,which is implemented by the superimposed image generation unit 305, isnot particularly limited, and a publicly-known image processingtechnology is applicable. The superimposed image generation unit 305outputs data of the generated superimposed image to the superimposedimage output unit 307 described below. The superimposed image generationunit 305 may associate the data of the generated superimposed image witha timestamp of date and time at which the image data has been generatedand store the data associated with the timestamp as history informationin the storage unit 311 described below.

The superimposed image output unit 307 is realized by, for example, aCPU, a ROM, a RAM, an output device, and a communication device. Thesuperimposed image output unit 307 outputs the superimposed imagegenerated by the superimposed image generation unit 305. Morespecifically, the superimposed image output unit 307 may output the dataof the generated superimposed image to various kinds of image servers orthe like provided outside the camera control unit 30 or may record thedata in a publicly-known recording medium. The superimposed image outputunit 307 may display the generated superimposed image on various kindsof display devices via the display control unit 309 described below inreal time.

The display control unit 309 is realized by, for example, a CPU, a ROM,a RAM, an output device, and a communication device. The display controlunit 309 performs display control when the superimposed image generatedby the superimposed image generation unit 305 is displayed on an outputdevice such as the display included in the camera control unit 30, anoutput device provided outside the camera control unit 30, or the like.With this, a user of the image pickup device 10 can instantly see adesired superimposed image.

The storage unit 311 is realized by, for example, a RAM, a storagedevice, or the like included in the camera control unit 30 according tothe embodiment. In the storage unit 311, for example, various kinds ofdata to be used by the camera control unit 30 according to theembodiment to control the image pickup device 10 are recorded. Thestorage unit 311 records, as appropriate, various parameters to bestored when the camera control unit 30 according to the embodimentperforms some processing and progress of the processing, various kindsof databases and programs, or the like.

The image pickup device control unit 301, the image data acquisitionunit 303, the superimposed image generation unit 305, the superimposedimage output unit 307, the display control unit 309, and the like canfreely perform read/write processing of data in the storage unit 311that stores such various kinds of information.

Heretofore, an example of the function of the camera control unit 30according to the embodiment has been described. Each of the structuralelements described above may be configured using a general-purposematerial or circuit or may be configured by hardware dedicated to thefunction of each structural element. Further, all the functions of thestructural elements may be performed by a CPU or the like. Accordingly,the configuration to be used can be changed as appropriate in accordancewith the technical level at the time of carrying out the presentembodiment.

Note that a computer program for realizing each function of the abovecamera control unit 30 according to the embodiment can be prepared andmounted on a personal computer or the like. It is also possible toprovide a computer readable recording medium in which such a computerprogram is stored. The recording medium is, for example, a magneticdisk, an optical disk, a magneto-optical disk, or a flash memory. Forexample, the above computer program may also be distributed via anetwork, instead of using the recording medium.

<Microscope Image Pickup System Including Image Pickup Device>

A microscope image pickup system 1000 including the image pickup device10 according to the embodiment will be briefly described with referenceto FIG. 6. FIG. 6 is an explanatory diagram schematically illustratingan example of a configuration of a microscope image pickup systemincluding the image pickup device according to the embodiment.

The microscope image pickup system can be constructed by combining theimage pickup device 10 described above (more specifically, the 2-piececamera system including the image pickup device 10) and a microscopeoptical system.

As schematically illustrated in FIG. 6, the microscope image pickupsystem 1000 includes the image pickup device 10, the CCU 30, the displaydevice 40, and a microscope optical system 50.

Herein, the image pickup device 10, the CCU 30, and the display device40 have configurations similar to the configurations thereof included inthe 2-piece camera system described above and therefore have similareffects. Thus, hereinafter, detailed description thereof will beomitted.

As schematically illustrated in FIG. 6, the microscope optical system 50includes a light source 501, a stage 503, an objective lens 505, arevolver 507, and a lens barrel 509, and the lens barrel 509 mainlyincludes an eyepiece lens 511, an imaging lens 513, and a beam splitterBS.

Illumination light emitted from the light source 501 is reflected by amirror M or the like as appropriate to be guided to a sample S placed onthe stage 503. The objective lens 505 forms a magnified image of thissample. The beam splitter BS provided in the lens barrel reflects a partof the image of the sample imaged by the objective lens 505 and guidesthe part to the eyepiece lens 511. The guided image of the sample isemitted to be substantially afocal by the eyepiece lens 511. With this,an observer of the microscope optical system 50 can observe themagnified image of the sample with the naked eye.

Meanwhile, the imaging lens 513 provided in the lens barrel 509 imagesthe image of the sample transmitted through the beam splitter BS on thevisible light image pickup element 111 and the fluorescence image pickupelement 117 of the image pickup device 10.

The revolver 507 has a function of holding the objective lens 505 on anobservation optical axis of the microscope, and the lens can be switchedto another objective lens 505 attached to the revolver 507 by operatinga rotating mechanism of the revolver 507.

A generation amount A of axial chromatic aberration between visiblelight and fluorescence is changed when the objective lens 505 is changedas described above.

Hereinafter, a focusing method using the fluorescence image focusingmechanism 119 will be briefly described. A visible light image can befocused by moving the stage 503 or the objective lens 505 upward anddownward in an optical axis direction to change a working distance. Atthis time, in the objective lens 505, axial chromatic aberration isgenerally corrected only in the visible light wavelength band, andtherefore axial chromatic aberration in the near-infrared fluorescencewavelength band is not corrected in many cases. In the case where onlythe visible light image is focused, a fluorescence image is blurred.Therefore, the fluorescence image is focused by the fluorescence imagefocusing mechanism 119 described above. With this, it is possible tofocus the fluorescence image while the visible light image is in afocused state.

Those captured images generated as described above are output to the CCU30, and the CCU 30 superimposes the images to thereby generate asuperimposed image. The generated superimposed image is displayed on thedisplay device 40 under the control of the CCU 30.

Heretofore, the microscope image pickup system 1000 including the imagepickup device 10 according to the embodiment has been briefly describedwith reference to FIG. 6.

<Another Example of Configuration of Image Pickup Device>

The image pickup device 10 according to the embodiment described aboveis attachable to, for example, various kinds of medical endoscopes suchas a rigid endoscope and various kinds of industrial endoscopes.Hereinafter, a medical endoscope will be exemplified and a configurationof the image pickup device 10 attachable to the medical endoscope willbe briefly described with reference to FIG. 7A and FIG. 7B. FIG. 7A andFIG. 7B are explanatory diagrams each of which schematically illustratesanother example of the configuration of the image pickup deviceaccording to the embodiment.

In the case where the image pickup device 10 according to the embodimentis connected to various kinds of endoscopes such as a rigid endoscope,as illustrated in FIG. 7A and FIG. 7B, a coupler optical system 25 inwhich axial chromatic aberration has been corrected at least in thevisible light wavelength band is attached as an imaging lens at a formerstage of the image pickup device 10. With this, an aerial image of ameasurement target object (for example, an affected part on which afluorescent probe is accumulated) generated by the endoscope can beconnected to the image pickup device 10.

As illustrated in FIG. 7A and FIG. 7B, a visible light image focusingmechanism 121 is provided for the coupler optical system 25 in the imagepickup device 10 to be attached to the endoscope. The visible lightimage focusing mechanism 121 is a mechanism for moving only the coupleroptical system 25 in the optical axis direction to focus a visible lightimage on the visible light image pickup element 111.

As the visible light image focusing mechanism 121, for example, anactuator such as a stepping motor or a piezoelectric element can beused, or a cam mechanism or the like can be used.

Note that, in FIG. 7A and FIG. 7B, the configurations of the imagepickup device 10 excluding the visible light image focusing mechanism121 are similar to the cases illustrated in FIG. 1A and FIG. 1B, exceptthat the optical unit 11 in FIG. 7A further includes the coupler opticalsystem 25. Therefore, hereinafter, detailed description thereof will beomitted.

<Endoscope Image Pickup System Including Image Pickup Device>

An endoscope image pickup system 2000 including the image pickup device10 illustrated in FIG. 7A and FIG. 7B will be briefly described withreference to FIG. 8. FIG. 8 is an explanatory diagram schematicallyillustrating an example of a configuration of an endoscope image pickupsystem including the image pickup device according to the embodiment.

The endoscope image pickup system can be constructed by combining theimage pickup device 10 described above (more specifically, the 2-piececamera system including the image pickup device 10) and an endoscopeoptical system.

As schematically illustrated in FIG. 8, the endoscope image pickupsystem 2000 includes the image pickup device 10 illustrated in FIG. 7Aor FIG. 7B, the CCU 30, the display device 40, and an endoscope opticalsystem 60.

Herein, the image pickup device 10, the CCU 30, and the display device40 have configurations similar to the configurations thereof describedabove and therefore have similar effects. Thus, hereinafter, detaileddescription thereof will be omitted.

The endoscope (rigid endoscope) optical system 60 includes an objectivelens 601, a plurality of relay lenses 603, and an eyepiece lens 605 inorder from an object side (subject side). The objective lens 601 formsan aerial image of a subject, and the relay lenses 603 performsunmagnified relay imaging of the formed aerial image multiple times.Thereafter, the eyepiece lens 605 performs afocal imaging of the lastaerial image, and thus the aerial image can be observed with the nakedeye.

Herein, the endoscope (rigid endoscope) is mainly for observing anaerial image with the naked eye, and therefore, in order to image theaerial image generated by the endoscope optical system 60 on the imagepickup element of the image pickup device 10, the coupler optical system25 serving as the imaging lens is disposed between the eyepiece lens 605and the image pickup device 10.

A focusing method using the fluorescence image focusing mechanism 119and the visible light image focusing mechanism 121 will be brieflydescribed.

In the endoscope image pickup system 2000 according to the embodiment,first, the visible light image focusing mechanism 121 moves only thecoupler optical system 25 in the optical axis direction to thereby focusa visible light image. In the coupler optical system 25, axial chromaticaberration is corrected only in the visible light wavelength band asdescribed above, and therefore a fluorescence image is not appropriatelyfocused and is blurred. After the visible light image focusing mechanism121 focuses the visible light image, the fluorescence image focusingmechanism 119 changes the isolation distance Δ between the optical unit11 to which the coupler optical system 25 is integrally attached and thefluorescence image pickup element 117, thereby focusing the fluorescenceimage. With this, it is possible to focus the fluorescence image whilethe visible light image is in a focused state.

Those captured images generated as described above are output to the CCU30, and the CCU 30 superimposes the images to thereby generate asuperimposed image. The generated superimposed image is displayed on thedisplay device 40 under the control of the CCU 30.

Heretofore, the endoscope image pickup system 2000 including the imagepickup device 10 according to the embodiment has been briefly describedwith reference to FIG. 8.

(Hardware Configuration)

Next, the hardware configuration of the camera control unit (CCU) 30according to the embodiment of the present disclosure will be describedin detail with reference to FIG. 9. FIG. 9 is a block diagram forillustrating the hardware configuration of the CCU 30 according to theembodiment of the present disclosure.

The CCU 30 mainly includes a CPU 901, a ROM 903, and a RAM 905.Furthermore, the CCU 30 also includes a host bus 907, a bridge 909, anexternal bus 911, an interface 913, an input device 915, an outputdevice 917, a storage device 919, a drive 921, a connection port 923,and a communication device 925.

The CPU 901 serves as an arithmetic processing apparatus and a controldevice, and controls the overall operation or a part of the operation ofthe CCU 30 according to various programs recorded in the ROM 903, theRAM 905, the storage device 919, or a removable recording medium 927.The ROM 903 stores programs, operation parameters, and the like used bythe CPU 901. The RAM 905 primarily stores programs that the CPU 901 usesand parameters and the like varying as appropriate during the executionof the programs. These are connected with each other via the host bus907 configured from an internal bus such as a CPU bus or the like.

The host bus 907 is connected to the external bus 911 such as a PCI(Peripheral Component Interconnect/Interface) bus via the bridge 909.

The input device 915 is an operation mechanism operated by a user, suchas a mouse, a keyboard, a touch panel, buttons, a switch and a lever.Also, the input device 915 may be a remote control mechanism (aso-called remote control) using, for example, infrared light or otherradio waves, or may be an externally connected apparatus 929 such as amobile phone or a PDA conforming to the operation of the CCU 30.Furthermore, the input device 915 generates an input signal based on,for example, information which is input by a user with the aboveoperation mechanism, and is configured from an input control circuit foroutputting the input signal to the CPU 901. The user of the CCU 30 caninput various data to the CCU 30 and can instruct the informationprocessing apparatus 10 to perform processing by operating this inputapparatus 915.

The output device 917 is configured from a device capable of visually oraudibly notifying acquired information to a user. Examples of suchdevice include display devices such as a CRT display device, a liquidcrystal display device, a plasma display device, an EL display deviceand lamps, audio output devices such as a speaker and a headphone, aprinter, a mobile phone, a facsimile machine, and the like. For example,the output device 917 outputs a result obtained by various processingsperformed by the CCU 30. More specifically, the display device displays,in the form of texts or images, a result obtained by various processesperformed by the CCU 30. On the other hand, the audio output deviceconverts an audio signal such as reproduced audio data and sound datainto an analog signal, and outputs the analog signal.

The storage device 919 is a device for storing data configured as anexample of a storage unit of the CCU 30. The storage device 919 isconfigured from, for example, a magnetic storage device such as a HDD(Hard Disk Drive), a semiconductor storage device, an optical storagedevice, or a magneto-optical storage device. This storage device 919stores programs to be executed by the CPU 901, various data, and variousdata obtained from the outside.

The drive 921 is a reader/writer for recording medium, and is embeddedin the CCU 30 or attached externally thereto. The drive 921 readsinformation recorded in the attached removable recording medium 927 suchas a magnetic disk, an optical disk, a magneto-optical disk, or asemiconductor memory, and outputs the read information to the RAM 905.Furthermore, the drive 921 can write in the attached removable recordingmedium 927 such as a magnetic disk, an optical disk, a magneto-opticaldisk, or a semiconductor memory. The removable recording medium 927 is,for example, a DVD medium, an HD-DVD medium, or a Blu-ray (registeredtrademark) medium. The removable recording medium 927 may be aCompactFlash (CF; registered trademark), a flash memory, an SD memorycard (Secure Digital Memory Card), or the like. Alternatively, theremovable recording medium 927 may be, for example, an IC card(Integrated Circuit Card) equipped with a non-contact IC chip or anelectronic appliance.

The connection port 923 is a port for allowing devices to directlyconnect to the CCU 30. Examples of the connection port 923 include a USB(Universal Serial Bus) port, an IEEE1394 port, a SCSI (Small ComputerSystem Interface) port, and the like. Other examples of the connectionport 923 include an RS-232C port, an optical audio terminal, an HDMI(High-Definition Multimedia Interface) port, and the like. By theexternally connected apparatus 929 connecting to this connection port923, the CCU 30 directly obtains various data from the externallyconnected apparatus 929 and provides various data to the externallyconnected apparatus 929.

The communication device 925 is a communication interface configuredfrom, for example, a communication device for connecting to acommunication network 931. The communication device 925 is, for example,a wired or wireless LAN (Local Area Network), Bluetooth (registeredtrademark), a communication card for WUSB (Wireless USB), or the like.Alternatively, the communication device 925 may be a router for opticalcommunication, a router for ADSL (Asymmetric Digital Subscriber Line), amodem for various communications, or the like. This communication device925 can transmit and receive signals and the like in accordance with apredetermined protocol such as TCP/IP on the Internet and with othercommunication devices, for example. The communication network 931connected to the communication device 925 is configured from a networkand the like, which is connected via wire or wirelessly, and may be, forexample, the Internet, a home LAN, infrared communication, radio wavecommunication, satellite communication, or the like.

Heretofore, an example of the hardware configuration capable ofrealizing the functions of the CCU 30 according to the embodiment of thepresent disclosure has been shown. Each of the structural elementsdescribed above may be configured using a general-purpose material, ormay be configured from hardware dedicated to the function of eachstructural element. Accordingly, the hardware configuration to be usedcan be changed as appropriate according to the technical level at thetime of carrying out the present embodiment.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design re-quirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

In addition, the effects described in the present specification aremerely illustrative and demonstrative, and not limitative. In otherwords, the technology according to the present disclosure can exhibitother effects that are evident to those skilled in the art along with orinstead of the effects based on the present specification.

Additionally, the present technology may also be configured as below.

(1)

A medical imaging device including:

a color separation prism that has a dichroic film configured to splitlight into first light belonging to a visible light wavelength band andsecond light belonging to a fluorescence wavelength band;

a fluorescence image sensor that is provided at an output side of thecolor separation prism and that is configured to image at least part ofthe second light belonging to the fluorescence wavelength band separatedby the dichroic film;

a visible light image sensor that is provided at the output side of thecolor separation prism and that is configured to image at least part ofthe first light belonging to the visible light wavelength band separatedby the dichroic film; and

a bandpass filter that is disposed between the color separation prismand the fluorescence image sensor,

wherein the fluorescence image sensor and the visible light image sensorare arranged such that an optical path difference between an opticalpath length of a fluorescence optical path for the second light imagedon the fluorescence image sensor via the color separation prism and anoptical path length of a visible light optical path for the first lightimaged on the visible light image sensor via the color separation prismcorresponds to an amount of a shift between a fluorescence imagingposition and a visible light imaging position, the shift being generatedby an imaging lens positioned at an input side of the color separationprism, and

wherein the fluorescence imaging position is an imaging position offiltered second light, which results from passing the second lightthrough the bandpass filter, such that the amount of shift is based onthe filtered second light.

(2)

The medical imaging device according to (1),

wherein each of the fluorescence image sensor and the visible lightimage sensor is fixed such that the optical path difference correspondsto the amount of the shift.

(3)

The medical imaging device according to (1),

wherein the fluorescence image sensor is provided such that an isolationdistance from the bandpass filter is changeable,

further including:

a fluorescence image focusing actuator configured to focus the secondlight belonging to the fluorescence wavelength band separated by thedichroic film on the fluorescence image sensor, and

wherein the fluorescence image focusing actuator controls the isolationdistance in accordance with the imaging lens attached at the input sideof the color separation prism such that the optical path differencecorresponds to the amount of the shift.

(4)

The medical imaging device according to (3),

wherein a coupler optical lens assembly, in which axial chromaticaberration has been corrected at least in the visible light wavelengthband, is provided as the imaging lens at the input side of the colorseparation prism,

wherein the fluorescence image sensor is provided such that theisolation distance from the bandpass filter is changeable,

wherein the image sensor further includes a visible light image focusingactuator configured to focus the first light belonging to the visiblelight wavelength band separated by the dichroic film on the visiblelight image sensor,

wherein the visible light image focusing actuator moves the coupleroptical lens assembly in an optical axis direction to focus the firstlight belonging to the visible light wavelength band separated by thedichroic film on the visible light image sensor, and

wherein the fluorescence image focusing actuator controls the isolationdistance such that the optical path difference, obtained when the firstlight belonging to the visible light wavelength band is focused on thevisible light image sensor, corresponds to the amount of the shift.

(5)

The medical imaging device according to (3)-(4),

wherein the fluorescence image focusing actuator controls the isolationdistance by moving the bandpass filter in an optical axis direction withrespect to the fluorescence image sensor.

(6)

The medical imaging device according to (3)-(5),

wherein the fluorescence image focusing actuator controls the isolationdistance by moving the fluorescence image sensor in an optical axisdirection with respect to the bandpass filter.

(7)

The medical imaging device according to (1)-(6),

wherein the dichroic film splits incident light into the second lightbelonging to a predetermined fluorescence wavelength band, light of aband of longer wavelengths than the predetermined fluorescencewavelength band, and light belonging to a band of shorter wavelengthsthan the predetermined fluorescence wavelength band.

(8)

The medical imaging device according to (1)-(7),

wherein the color separation prism is a prism comprising a first prismon which the first light belonging to the visible light wavelength bandand the second light belonging to the fluorescence wavelength band areincident, the first prism functioning as the visible light optical paththrough which the first light belonging to the visible light wavelengthband is guided, and

a second prism functioning as the fluorescence optical path throughwhich the second light belonging to the fluorescence wavelength band isguided, to each other,

wherein the first prism and the second prism are joined to each othervia the dichroic film,

wherein the second light belonging to the fluorescence wavelength bandseparated by the dichroic film moves straight in the second prism to bevertically incident on the bandpass filter, and

wherein the first light belonging to the visible light wavelength bandseparated by the dichroic film is totally reflected in the first prismand is then imaged on the visible light image sensor.

(9)

The medical imaging device according to (1)-(8), further including a3-color separation prism configured to split the first light belongingto the visible light wavelength band emitted from the color separationprism into three colors of an R component, a G component, and a Bcomponent.

(10)

The medical imaging device according to (1)-(9),

wherein the dichroic film has transmittance of 90% or more in awavelength band from 780 nm to 880 nm and has transmittance of 10% orless in a wavelength band from 400 nm to 720 nm.

(11)

The medical imaging device according to (1)-(10),

wherein the bandpass filter has transmittance of 90% or more in awavelength band from 820 nm to 850 nm and has transmittance of 10% orless in a wavelength band from 400 nm to 805 nm and in a wavelength bandfrom 860 nm to 1000 nm.

(12)

A medical microscopic system including:

a microscopic optical lens assembly including at least an objective lensand an imaging lens; and

an imaging device configured to capture a magnified image of an object,

wherein the imaging device includes

a color separation prism that has a dichroic film configured to splitlight into first light belonging to the visible light wavelength bandand second light belonging to the fluorescence wavelength band,

a fluorescence image sensor that is provided at an output side of thecolor separation prism and that is configured to image at least part ofthe second light belonging to the fluorescence wavelength band separatedby the dichroic film,

a visible light image sensor that is provided at the output side of thecolor separation prism and that is configured to image at least part ofthe first light belonging to the visible light wavelength band separatedby the dichroic film, and

a bandpass filter that is disposed between the color separation prismand the fluorescence image sensor,

wherein the fluorescence image sensor and the visible light image sensorare arranged such that an optical path difference between an opticalpath length of a fluorescence optical path for the second light imagedon the fluorescence image sensor via the color separation prism and anoptical path length of a visible light optical path for the first lightimaged on the visible light image sensor via the color separation prismcorresponds to an amount of a shift between a fluorescence imagingposition and a visible light imaging position, the shift being generatedby an imaging lens positioned at an input side of the color separationprism, and

wherein the fluorescence imaging position is an imaging position offiltered second light, which results from passing the second lightthrough the bandpass filter, such that the amount of shift is based onthe filtered second light.

(13)

The medical microscope imaging system according to (12),

wherein each of the fluorescence image sensor and the visible lightimage sensor is fixed such that the optical path difference correspondsto the amount of the shift.

(14)

The medical microscope imaging system according to (12),

wherein the fluorescence image sensor is provided such that an isolationdistance from the bandpass filter is changeable,

wherein the imaging device further includes a fluorescence imagefocusing actuator configured to focus the second light belonging to thefluorescence wavelength band separated by the dichroic film on thefluorescence image sensor, and

wherein the fluorescence image focusing actuator controls the isolationdistance in accordance with the imaging lens attached at the input sideof the color separation prism such that the optical path differencecorresponds to the amount of the shift.

(15)

The medical microscope imaging system according to (14),

wherein a coupler optical lens assembly, in which axial chromaticaberration has been corrected at least in the visible light wavelengthband, is provided as the imaging lens at the input side of the colorseparation prism,

wherein the fluorescence image sensor is provided such that theisolation distance from the bandpass filter is changeable,

wherein the image sensor further includes a visible light image focusingactuator configured to focus the first light belonging to the visiblelight wavelength band separated by the dichroic film on the visiblelight image sensor,

wherein the visible light image focusing actuator moves the coupleroptical lens assembly in an optical axis direction to focus the firstlight belonging to the visible light wavelength band separated by thedichroic film on the visible light image sensor, and

wherein the fluorescence image focusing actuator controls the isolationdistance such that the optical path difference, obtained when the firstlight belonging to the visible light wavelength band is focused on thevisible light image sensor, corresponds to the amount of the shift.

(16)

The medical microscope imaging system according to (14)-(15),

wherein the fluorescence image focusing actuator controls the isolationdistance by moving the bandpass filter in an optical axis direction withrespect to the fluorescence image sensor or moving the fluorescenceimage sensor in an optical axis direction with respect to the bandpassfilter.

(17)

The medical microscope imaging system according to (12)-(16),

wherein the color separation prism is a prism comprising

a first prism on which the first light belonging to the visible lightwavelength band and the second light belonging to the fluorescencewavelength band are incident, the first prism functioning as the visiblelight optical path through which the first light belonging to thevisible light wavelength band is guided, and

a second prism functioning as the fluorescence optical path throughwhich the second light belonging to the fluorescence wavelength band isguided, to each other,

wherein the first prism and the second prism are joined to each othervia the dichroic film,

wherein the second light belonging to the fluorescence wavelength bandseparated by the dichroic film moves straight in the second prism to bevertically incident on the bandpass filter, and

wherein the first light belonging to the visible light wavelength bandseparated by the dichroic film is totally reflected in the first prismand is then imaged on the visible light image sensor.

(18)

The medical microscope imaging system according to (12)-(17),

wherein the dichroic film has transmittance of 90% or more in awavelength band from 780 nm to 880 nm and has transmittance of 10% orless in a wavelength band from 400 nm to 720 nm.

(19)

The medical microscope imaging system according to (12)-(18),

wherein the bandpass filter has transmittance of 90% or more in awavelength band from 820 nm to 850 nm and has transmittance of 10% orless in a wavelength band from 400 nm to 805 nm and in a wavelength bandfrom 860 nm to 1000 nm.

(20)

An endoscopic system including:

an endoscopic optical lens assembly;

an imaging device configured to capture an image of an object; and

an coupler optical lens assembly that is provided between the endoscopicoptical lens assembly and the imaging device,

wherein the imaging device includes

a color separation prism that has a dichroic film configured to splitlight into first light belonging to the visible light wavelength bandand second light belonging to the fluorescence wavelength band,

a fluorescence image sensor that is provided at an output side of thecolor separation prism and that is configured to image at least part ofthe second light belonging to the fluorescence wavelength band separatedby the dichroic film,

a visible light image sensor that is provided at the output side of thecolor separation prism and that is configured to image at least part ofthe first light belonging to the visible light wavelength band separatedby the dichroic film, and

a bandpass filter that is disposed between the color separation prismand the fluorescence image sensor, and

wherein the fluorescence image sensor and the visible light image sensorare arranged such that an optical path difference between an opticalpath length of a fluorescence optical path for the second light imagedon the fluorescence image sensor via the color separation prism and anoptical path length of a visible light optical path for the first lightimaged on the visible light image sensor via the color separation prismcorresponds to an amount of a shift between a fluorescence imagingposition and a visible light imaging position, the shift being generatedby an imaging lens positioned at an input side of the color separationprism, and

wherein the fluorescence imaging position is an imaging position offiltered second light, which results from passing the second lightthrough the bandpass filter, such that the amount of shift is based onthe filtered second light.

REFERENCE SIGNS LIST

-   -   10 image pickup device    -   20 imaging lens    -   30 camera control unit (CCU)    -   40 display device    -   50 microscope optical system    -   60 endoscope optical system    -   101 color separation prism    -   103 dichroic film    -   105 first prism    -   107 second prism    -   111 image pickup element for capturing visible light image    -   113 infrared cut-off filter    -   115 bandpass filter    -   117 fluorescence image pickup element    -   119 fluorescence image focusing mechanism    -   121 visible light image focusing mechanism    -   1000 microscope image pickup system    -   2000 endoscope image pickup system

The invention claimed is:
 1. A medical imaging device comprising: acolor separation prism that has a dichroic film configured to splitlight into first light belonging to a visible light wavelength band andsecond light belonging to a fluorescence wavelength band; a fluorescenceimage sensor that is provided at an output side of the color separationprism and that is configured to image at least part of the second lightbelonging to the fluorescence wavelength band separated by the dichroicfilm; a visible light image sensor that is provided at the output sideof the color separation prism and that is configured to image at leastpart of the first light belonging to the visible light wavelength bandseparated by the dichroic film; and a bandpass filter that is disposedbetween the color separation prism and the fluorescence image sensor,wherein the fluorescence image sensor and the visible light image sensorare arranged such that an optical path difference between an opticalpath length of a fluorescence optical path for the second light imagedon the fluorescence image sensor via the color separation prism and anoptical path length of a visible light optical path for the first lightimaged on the visible light image sensor via the color separation prismcorresponds to an amount of a shift between a fluorescence imagingposition and a visible light imaging position, the shift being generatedby an imaging lens positioned at an input side of the color separationprism, and wherein the fluorescence imaging position is an imagingposition of filtered second light, which results from passing the secondlight through the bandpass filter, such that the amount of shift isbased on the filtered second light.
 2. The medical imaging deviceaccording to claim 1, wherein each of the fluorescence image sensor andthe visible light image sensor is fixed such that the optical pathdifference corresponds to the amount of the shift.
 3. The medicalimaging device according to claim 1, wherein the fluorescence imagesensor is provided such that an isolation distance from the bandpassfilter is changeable, further comprising: a fluorescence image focusingactuator configured to focus the second light belonging to thefluorescence wavelength band separated by the dichroic film on thefluorescence image sensor, and wherein the fluorescence image focusingactuator controls the isolation distance in accordance with the imaginglens attached at the input side of the color separation prism such thatthe optical path difference corresponds to the amount of the shift. 4.The medical imaging device according to claim 3, wherein a coupleroptical lens assembly, in which axial chromatic aberration has beencorrected at least in the visible light wavelength band, is provided asthe imaging lens at the input side of the color separation prism,wherein the fluorescence image sensor is provided such that theisolation distance from the bandpass filter is changeable, wherein theimage sensor further includes a visible light image focusing actuatorconfigured to focus the first light belonging to the visible lightwavelength band separated by the dichroic film on the visible lightimage sensor, wherein the visible light image focusing actuator movesthe coupler optical lens assembly in an optical axis direction to focusthe first light belonging to the visible light wavelength band separatedby the dichroic film on the visible light image sensor, and wherein thefluorescence image focusing actuator controls the isolation distancesuch that the optical path difference, obtained when the first lightbelonging to the visible light wavelength band is focused on the visiblelight image sensor, corresponds to the amount of the shift.
 5. Themedical imaging device according to claim 3, wherein the fluorescenceimage focusing actuator controls the isolation distance by moving thebandpass filter in an optical axis direction with respect to thefluorescence image sensor.
 6. The medical imaging device according toclaim 3, wherein the fluorescence image focusing actuator controls theisolation distance by moving the fluorescence image sensor in an opticalaxis direction with respect to the bandpass filter.
 7. The medicalimaging device according to claim 1, wherein the dichroic film splitsincident light into the second light belonging to a predeterminedfluorescence wavelength band, light of a band of longer wavelengths thanthe predetermined fluorescence wavelength band, and light belonging to aband of shorter wavelengths than the predetermined fluorescencewavelength band.
 8. The medical imaging device according to claim 1,wherein the color separation prism is a prism comprising a first prismon which the first light belonging to the visible light wavelength bandand the second light belonging to the fluorescence wavelength band areincident, the first prism functioning as the visible light optical paththrough which the first light belonging to the visible light wavelengthband is guided, and a second prism functioning as the fluorescenceoptical path through which the second light belonging to thefluorescence wavelength band is guided, to each other, wherein the firstprism and the second prism are joined to each other via the dichroicfilm, wherein the second light belonging to the fluorescence wavelengthband separated by the dichroic film moves straight in the second prismto be vertically incident on the bandpass filter, and wherein the firstlight belonging to the visible light wavelength band separated by thedichroic film is totally reflected in the first prism and is then imagedon the visible light image sensor.
 9. The medical imaging deviceaccording to claim 1, further comprising a 3-color separation prismconfigured to split the first light belonging to the visible lightwavelength band emitted from the color separation prism into threecolors of an R component, a G component, and a B component.
 10. Themedical imaging device according to claim 1, wherein the dichroic filmhas transmittance of 90% or more in a wavelength band from 780 nm to 880nm and has transmittance of 10% or less in a wavelength band from 400 nmto 720 nm.
 11. The medical imaging device according to claim 1, whereinthe bandpass filter has transmittance of 90% or more in a wavelengthband from 820 nm to 850 nm and has transmittance of 10% or less in awavelength band from 400 nm to 805 nm and in a wavelength band from 860nm to 1000 nm.
 12. A medical microscopic system comprising: amicroscopic optical lens assembly including at least an objective lensand an imaging lens; and an imaging device configured to capture amagnified image of an object, wherein the imaging device includes acolor separation prism that has a dichroic film configured to splitlight into first light belonging to the visible light wavelength bandand second light belonging to the fluorescence wavelength band, afluorescence image sensor that is provided at an output side of thecolor separation prism and that is configured to image at least part ofthe second light belonging to the fluorescence wavelength band separatedby the dichroic film, a visible light image sensor that is provided atthe output side of the color separation prism and that is configured toimage at least part of the first light belonging to the visible lightwavelength band separated by the dichroic film, and a bandpass filterthat is disposed between the color separation prism and the fluorescenceimage sensor, wherein the fluorescence image sensor and the visiblelight image sensor are arranged such that an optical path differencebetween an optical path length of a fluorescence optical path for thesecond light imaged on the fluorescence image sensor via the colorseparation prism and an optical path length of a visible light opticalpath for the first light imaged on the visible light image sensor viathe color separation prism corresponds to an amount of a shift between afluorescence imaging position and a visible light imaging position, theshift being generated by an imaging lens positioned at an input side ofthe color separation prism, and wherein the fluorescence imagingposition is an imaging position of filtered second light, which resultsfrom passing the second light through the bandpass filter, such that theamount of shift is based on the filtered second light.
 13. The medicalmicroscope imaging system according to claim 12, wherein each of thefluorescence image sensor and the visible light image sensor is fixedsuch that the optical path difference corresponds to the amount of theshift.
 14. The medical microscope imaging system according to claim 12,wherein the fluorescence image sensor is provided such that an isolationdistance from the bandpass filter is changeable, wherein the imagingdevice further includes a fluorescence image focusing actuatorconfigured to focus the second light belonging to the fluorescencewavelength band separated by the dichroic film on the fluorescence imagesensor, and wherein the fluorescence image focusing actuator controlsthe isolation distance in accordance with the imaging lens attached atthe input side of the color separation prism such that the optical pathdifference corresponds to the amount of the shift.
 15. The medicalmicroscope imaging system according to claim 14, wherein a coupleroptical lens assembly, in which axial chromatic aberration has beencorrected at least in the visible light wavelength band, is provided asthe imaging lens at the input side of the color separation prism,wherein the fluorescence image sensor is provided such that theisolation distance from the bandpass filter is changeable, wherein theimage sensor further includes a visible light image focusing actuatorconfigured to focus the first light belonging to the visible lightwavelength band separated by the dichroic film on the visible lightimage sensor, wherein the visible light image focusing actuator movesthe coupler optical lens assembly in an optical axis direction to focusthe first light belonging to the visible light wavelength band separatedby the dichroic film on the visible light image sensor, and wherein thefluorescence image focusing actuator controls the isolation distancesuch that the optical path difference, obtained when the first lightbelonging to the visible light wavelength band is focused on the visiblelight image sensor, corresponds to the amount of the shift.
 16. Themedical microscope imaging system according to claim 14, wherein thefluorescence image focusing actuator controls the isolation distance bymoving the bandpass filter in an optical axis direction with respect tothe fluorescence image sensor or moving the fluorescence image sensor inan optical axis direction with respect to the bandpass filter.
 17. Themedical microscope imaging system according to claim 12, wherein thecolor separation prism is a prism comprising a first prism on which thefirst light belonging to the visible light wavelength band and thesecond light belonging to the fluorescence wavelength band are incident,the first prism functioning as the visible light optical path throughwhich the first light belonging to the visible light wavelength band isguided, and a second prism functioning as the fluorescence optical paththrough which the second light belonging to the fluorescence wavelengthband is guided, to each other, wherein the first prism and the secondprism are joined to each other via the dichroic film, wherein the secondlight belonging to the fluorescence wavelength band separated by thedichroic film moves straight in the second prism to be verticallyincident on the bandpass filter, and wherein the first light belongingto the visible light wavelength band separated by the dichroic film istotally reflected in the first prism and is then imaged on the visiblelight image sensor.
 18. The medical microscope imaging system accordingto claim 12, wherein the dichroic film has transmittance of 90% or morein a wavelength band from 780 nm to 880 nm and has transmittance of 10%or less in a wavelength band from 400 nm to 720 nm.
 19. The medicalmicroscope imaging system according to claim 12, wherein the bandpassfilter has transmittance of 90% or more in a wavelength band from 820 nmto 850 nm and has transmittance of 10% or less in a wavelength band from400 nm to 805 nm and in a wavelength band from 860 nm to 1000 nm.
 20. Anendoscopic system comprising: an endoscopic optical lens assembly; animaging device configured to capture an image of an object; and ancoupler optical lens assembly that is provided between the endoscopicoptical lens assembly and the imaging device, wherein the imaging deviceincludes a color separation prism that has a dichroic film configured tosplit light into first light belonging to the visible light wavelengthband and second light belonging to the fluorescence wavelength band, afluorescence image sensor that is provided at an output side of thecolor separation prism and that is configured to image at least part ofthe second light belonging to the fluorescence wavelength band separatedby the dichroic film, a visible light image sensor that is provided atthe output side of the color separation prism and that is configured toimage at least part of the first light belonging to the visible lightwavelength band separated by the dichroic film, and a bandpass filterthat is disposed between the color separation prism and the fluorescenceimage sensor, and wherein the fluorescence image sensor and the visiblelight image sensor are arranged such that an optical path differencebetween an optical path length of a fluorescence optical path for thesecond light imaged on the fluorescence image sensor via the colorseparation prism and an optical path length of a visible light opticalpath for the first light imaged on the visible light image sensor viathe color separation prism corresponds to an amount of a shift between afluorescence imaging position and a visible light imaging position, theshift being generated by an imaging lens positioned at an input side ofthe color separation prism, and wherein the fluorescence imagingposition is an imaging position of filtered second light, which resultsfrom passing the second light through the bandpass filter, such that theamount of shift is based on the filtered second light.